A few years ago, I interviewed canon lawyer Edward Peters about a topic that is confusing and controversial to many people: excommunication.

“Excommunication has roots deep in ecclesiastical history, and it is still applied, in fact increasingly applied, today. But it’s more than a penalty for past actions; it’s really an urgent call to reform one’s conduct in the future,” he said. “Excommunication is classified as a ‘medicinal penalty’ by the Church precisely because its main purpose is to bring about reform in the individual. Having certain actions punished by excommunication demonstrates that certain actions are gravely wrong in themselves and cause deep harm both to their perpetrators and to others.”

Let’s begin with the Old Testament. Ezekiel was called by God to prophesy during the Babylonian exile (sixth century B.C.), to prepare his countrymen for bad news — the destruction of Jerusalem — and to proclaim good news — the promise of a new and everlasting covenant. Today’s reading from Ezekiel 33 repeats a message give in Chapter 3: The prophet was appointed to be a “watchman for the house of Israel” who would warn the wicked and try to save them from destruction. He was to be like the sentinel on the walls of a city warning of danger, or like the shepherd who looks after wayward sheep.

He was, in other words, to utter “an urgent call to reform one’s conduct.” What is especially striking is God’s declaration that if Ezekiel failed to warn the wicked man, he would be held responsible for that man’s death. Similarly, if he did provide a warning but was rebuffed by the unrepentant man, Ezekiel’s actions would still be accounted to his credit: “He shall die for his guilt, but you shall save yourself.” The modern concept of “live and let live” is foreign to the biblical perspective precisely because our actions affect the lives of others. God wishes no man to perish apart from divine life, for “God our Savior … wills everyone to be saved and to come to the knowledge of the truth” (1 Tm 2:3-4). So, with that in mind, all of us are responsible, in various ways, for helping others avoid sin and pursue holiness.

A specific example of this is described by Jesus in today’s Gospel, from a longer section (Mt 18) sometimes called the “ecclesiastical discourse.” The Greek word ekklesia is the root for “church”; it refers to an assembly gathered for a specific public purpose. It appears just twice in the Gospels: in Matthew 18:17 and in Matthew 16:18. In both cases, it is used in the specific context of apostolic authority and the ability to “bind and loose.” In today’s reading, the apostles are told how to handle a Christian who has sinned but refuses to reconcile with his fellow Christians and the Church. Since the Church is the household of God, it needs watchmen who are mindful of such dangers and shepherds who will work to bring wandering sheep back into the fold.

Those who refuse to listen to and submit to proper Church authority are to be kept from full communion for their sake and the sake of the Church. In other words, excommunication is meant to bring about reform on the part of the sinner and harmony within the Body of Christ. It is an act of love, meant to save the sinner from eternal spiritual destruction.